The wives of senior politicians have been detained on suspicion of being involved in a baby-trafficking network

* Case linked to "baby factories" in Nigeria

* Wives of top politicians among those detained

NIAMEY, June 26 (Reuters) - Authorities in Niger have detained 17 people, including wives of senior politicians, suspected of being involved in a baby-trafficking network, two legal sources said on Thursday.

The arrests follow an investigation by Niger's police into 30 people suspected of acquiring new-born babies from "baby factories" in neighbouring Nigeria. The case has been referred to Niger's public prosecutor.

Human trafficking and the sale of children is a long-standing issue across West Africa. Last year, Nigerian police raided several "baby factories", freeing dozens of pregnant girls who were being forced to bear children for sale.

"A judge has indicted and detained over a dozen people on charges of lying about giving birth, forgery and use of false documents," a court official said, requesting anonymity.

"It is related to baby factories in Nigeria," he added.

A second legal source said 17 people had been arrested and another person was being sought.

Among the detained is one of the wives of Hama Amadou, the president of Niger's national assembly and a key opposition figure, the first official said.

"I must say that my client, the wife of the President of the National Assembly, is presumed innocent until the court finds her guilty," Souley Oumarou, the lawyer acting for Hama Amadou's wife, told Reuters.

"This whole thing is a political witch-hunt," he said.

A wife of Niger's agriculture minister as well as a former bank director and his three wives were among those detained, the court official said.

Political tensions have risen in Niger since August when Amadou, who had been part of President Mahamadou Issoufou's coalition, fell out with the president.

Issoufou's government has accused Amadou and his Nigerien Democratic Movement (MODEN) party of trying to incite a military coup in the uranium-exporting West African nation.

Amadou is seen as the main challenger to Issoufou for the next presidential election, due in 2016. (Reporting by Abdoulaye Massalaki; Writing by Bate Felix; Editing by David Lewis and Andrew Roche)